[Tutor] puzzled by main()

[Dick Moores]

Should I have attached intSpell.py as a text file?

Dick Moores 
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def convertNToString(n):
    "convert integer to string"
    return str(n)


def regularizeFirstGroup(s):
    "prepend enough zeros, if any needed, to make a group of 3 digits: 45-> 045"
    if len(s) % 3 != 0:
        numOfZerosToPrepend = 3 - (len(s) % 3)
        stringOfZerosToPrepend = "0" * numOfZerosToPrepend
        s = stringOfZerosToPrepend + s
        return s
    else:
        return s

# example: illionNum of group "345" in "111345666000" is "2"
def ComputeIllionNum(s):
    "find illionNum of group"
    illionNum = len(s) / 3 - 1
    return illionNum

#example: illionName of group "111" in "111345666000" is "billion"
def illionNumToName(illionNum):
    "find illionName of group, given its illionNum"
    names = [ \
        "",
        "thousand",
        "million",
        "billion",
        "trillion",
        "quadrillion",
        "quintillion",
        "sextillion",
        "septillion",
        "octillion",
        "nonillion",
        "decillion",
        "undecillion",
        "duodecillion",
        "tredecillion",
        "quattuordecillion",
        "quindecillion",
        "sexdecillion",
        "septendecillion",
        "octodecillion",
        "novemdecillion",
        "vigintillion"]
    illionName = names[illionNum]
    return illionName

def extractGroup(s):
    "get group to work on"
    group = s[:3]
    return group

def stripFrontZeros(r):
    "strip zeros at front of group, if any. E.g., 045 -> 45, 003 -> 3"
    if int(r) == 0:
        return ""
    while r[0] == "0":
        r = r[1:]
    return r

def prepareGroupForPrinting(group):
    "use stripFrontZeros(group) on group"
    return stripFrontZeros(group)


def main():
    s = convertNToString(n)
    s = regularizeFirstGroup(s)
    a = ""
    # work on each group in turn, from first group to end group of s
    for index in range(0,len(s),3):
        illionNum = ComputeIllionNum(s[index:])
        illionName = illionNumToName(illionNum)
        group = extractGroup(s[index:])
        group = prepareGroupForPrinting(group)
        # don't print illionName if group is originally "000"
        if group == "":
            illionName = ""
            continue
        a = a + " " + group + " " + illionName + ","
    # remove final " ," or ","
    if a[-2:] == " ,":
        a = a[:-2]    
    else:
        a = a[:-1]
    answer = a
    return answer

if __name__=='__main__':
    n = 12008787987   
    print main()